1. Field of the Invention
This invention relates to silicon carbide material used in immersed heater protection tubes used in smelting furnace for low-melting point metals such as aluminum, lead etc. and furnaces for holding these molten metals, temperature sensor protection tubes, tubes for gas blow-out operation, furnace liner materials and so on.
2. Description of the Prior Art
Hitherto, the heating of low-melting metals such as aluminum and lead for fusion, and holding these molten metals has been carried out by fusion or from the outer side of the smelting or molding bath. Recently, however, extensive use is made of a system, in which a heater is accommodated in a protective tube and immersed in the metal.
Hitherto, use has been made of cast iron formed with a protective film or sintered bodies of silicon carbide or graphite. The internal heating system, in which heating is carried out by accommodating such a material as mentioned above and immersed in the metal, has a very superior thermal efficiency to the conventional external heating system. On the demerit side, however, since the aforementioned material is used in direct contact with the molten, it is liable to be attacked by the molten or an oxidation prevention agent floating on the molten surface. Further, the heat spalling is not always satisfactory, and long life cannot be expected.
The aforementioned materials are also used as temperature sensor protection tubes, operating tubes and other materials dealing with low-melting point fusion metals but presents similar problems.
Further, there are frequent occasions in which it is necessary to immerse these materials in the molten and take them out thereof. In such a case, formation of cracks or detachment of the protective film is prone due to a sudden temperature change.